Many people suffer from compression injury to the soft tissues of the wrist and carpal tunnel. These injuries may be produced in the workplace, e.g., by frequent, sustained repetitive motions involving the use of the hands, or may be associated with trauma to the hand or wrist, pre-existing medical conditions, hormonal changes, hereditary traits, and use of medical apparatus such as wheelchairs, and other factors (Gross et al, 2002). Without treatment, such injuries accumulate and lead to chronic neuromuscular disorders of the hand and the upper limb. The most familiar of these disorders is carpal tunnel syndrome, which is a growing public health issue that affects approximately 0.1% of the U.S. population (Hunter, Mackin and Callahan, Rehabilitation of the Hand and Upper Extremity. Fifth Edition, Mosby press, USA, 2002) and produces pain, discomfort, nerve conduction disturbances and impairment of function of the hand and sometimes the upper limb as well.
Carpal tunnel syndrome is caused by compression of the median nerve in the carpal tunnel. The median nerve receives blood, oxygen and nutrients through a microvasculature network which is present in the connective tissue surrounding the nerve fiber. An increased pressure on the nerve fiber constricts the microvessels and reduces the blood flow to the nerve. Prolonged deprivation of oxygen and nutrients will result in severe nerve damage.
The carpal tunnel is a confined anatomic space defined by the transverse carpal ligament on the palmar (anterior) side of the hand and by a semicircular bony ledge comprised of the carpal wrist bones on the dorsal and lateral sides of the hand. The tunnel serves as a conduit for the median nerve, blood vessels, and tendons which supply the extrinsic hand muscles.
An increase in the volume of the carpal contents or a decrease in the cross-sectional area of the carpal tunnel will increase the hydrostatic (interstitial) pressure in the tunnel and can potentially lead to compression damage to the median nerve. For example, conditions that irritate or inflame the tendons can cause them to swell and exert pressure on the median nerve. The increase in volume of the tendons and the median nerve, when inflamed, can increase the likelihood of carpal tunnel symptoms. A thickening of the transverse carpal ligament or of the bones a butting the carpal tunnel can reduce cross-sectional area of the tunnel. The tunnel cross-sectional area also changes with wrist position. Wrist flexion or extension decreases the cross-sectional area, and increases the hydrostatic pressure of the tunnel. Most wrist flexion occurs around the lateral axis of the radiocarpal joint, whereas most wrist extension occurs around the lateral axis of the midcarpal joint. Wrist flexion causes the flexor tendons to rearrange so they are more likely to compress the median nerve. The median nerve responds by rearranging its position between the superficial flexor tendons (Skie et al, J. Hand Surgery [Am] 15: 934–939 (1990)). The carpal tunnel cross-sectional area is smaller in carpal tunnel syndrome patients compared with asymptomatic control populations.
Carpal tunnel syndrome may be treated by non-surgical and surgical means. In early stages of development, therapies are directed to alleviating symptoms and preventing the occurrence of more severe symptoms. Such therapies include: restricting the motion of the wrist by means of wrist braces and splints, controlling swelling of soft tissue structures by administering anti-inflammatory medications, sometimes injecting steroids locally into the carpal tunnel; applying heat or cold to the affected site to promote repair of injured tissues; providing exercises to increase circulation, speed recovery and increase the range of motion of the wrist; and avoiding activities that produced the symptoms initially. Surgery, which may involve cutting the transverse carpal ligament to relieve pressure on the median nerve, may be necessary if the symptoms are severe and/or if the non-surgical therapies do not resolve the problem. Non-surgical therapies are reported to be effective in relieving symptoms of 86% of afflicted patients (Benefice, 1994).
The present invention is drawn to wrist brace technology for use by patients with existing carpal tunnel syndrome and related nerve entrapment disorders, and patients who are at risk for developing carpal tunnel syndrome and are in need of wrist support which allows motion of the fingers and palm.
The prior art wrist braces have one or more of the following drawbacks. They confine the wrist and forearm in a neutral position, but restrict the motion of the fingers required for daily activities; they enclose the hand, wrist and forearm in material which prevents air from circulating to the underlying tissues and promotes accumulation of moisture, bacteria and dirt between the brace and the tissue; they are difficult to attach to the hand and bulky to wear under clothing; they exert pressure on flexor tendons and the median nerve; and if made from a rigid material, they are uncomfortable to wear, develop unpleasant odors and have an anatomically incorrect shape.
U.S. Pat. No. 6,540,710 discloses a one piece molded plastic wrist brace that is designed to hold the wrist in a neutral position, block wrist flexion, extension, and ulnar/radial deviations, and limit hand movement without compressing the anterior forearm and flexor tendons.